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Abstract:

A method (and system and server) in which, when a mobile phone
unauthorized by a data server requests an access to a document stored in
the data server, the unauthorized mobile phone sends a request for access
permit to an authorized mobile phone. The authorized mobile phone sends
back information for temporary access to the unauthorized mobile phone.
On the basis of the information for temporary access, the unauthorized
mobile phone transmits a request for temporary access to the data server,
upon which the data server transmits information for judgment to the
authorized mobile phone. On the basis of the information for judgment,
the authorized mobile phone judges whether the unauthorized mobile phone
should be permitted an access to the requested document. The unauthorized
mobile phone is granted a temporary access to the requested document if
the document is currently displayed on the authorized mobile phone.

Claims:

1. A document browsing system comprising a data server and multiple
communication terminals having image data displaying function, A. the
communication terminals comprising: an authorized communication terminal
that is authorized by an authenticator of the data server; and an
unauthorized communication terminal that is not authorized by the
authenticator; and B. the data server comprising: a storage device
storing document data; a data converter for converting the document data
to image data; the authenticator for authentication and authorization of
the communication terminals; a communicator for communicating with the
multiple communication terminals and sending the image data to the
authorized communication terminal; and a communication detector for
detecting the state of communication between the communication terminals,
wherein C. the authorized communication terminal transmits information
for temporary access to the unauthorized communication terminal upon
receipt of a request for access permit from the unauthorized
communication terminal requesting an access to the document data, the
information for temporary access being used for granting the unauthorized
communication terminal a temporary access permit, and exchanges
information with the data server to decide whether the unauthorized
communication terminal should be allowed to access the document data; the
unauthorized communication terminal transmits the request for access
permit to the authorized communication terminal when requesting an access
to the document data, produces a request for temporary access on the
basis of the information for temporary access as received from the
authorized communication terminal, and transmits the request for
temporary access to the data server; and the data server sends image data
of the same document data as sent to the authorized communication
terminal to the unauthorized communication terminal if the temporary
access of the unauthorized communication terminal to the document data is
permitted on the basis of the information exchanged between the data
server and the authorized communication terminal when the request for
temporary access is received from the unauthorized communication terminal
and the communication detector detects that the authorized communication
terminal is in communication with the unauthorized communication
terminal, and the data server invalidates the temporary access permit
given to the unauthorized communication terminal when the communication
detector detects the end of communication between the authorized
communication terminal and the unauthorized communication terminal.

2. The document browsing system as recited in claim 1, wherein A1. the
authorized communication terminal comprises: a first data producer for
producing the information for temporary access upon receipt of the
request for access permit from the unauthorized communication terminal; a
judging section for judging whether to grant the unauthorized
communication terminal the temporary access permit or not; and a first
controller for controlling the authorized communication terminal to
transmit the information for temporary access to the unauthorized
communication terminal and transmit the judgment by the judging section
to the data server; A2. the unauthorized communication terminal
comprises: a second data producer for producing the request for access
permit and, upon receipt of the information for temporary access from the
authorized communication terminal, the request for temporary access; and
a second controller for controlling the unauthorized communication
terminal to transmit the request for access permit to the authorized
communication terminal and transmit the request for temporary access to
the data server; and B. the data server further comprises: a third data
producer for producing information for judgment by the judging section in
the authorized communication terminal upon receipt of the request for
temporary access from the unauthorized communication terminal; and a
third controller for controlling the data server to transmit the
information for judgment to the authorized communication terminal, send
the image data of the document data to the unauthorized communication
terminal when the judgment received from the authorized communication
terminal permits the access and the authorized communication terminal is
in communication with the unauthorized communication terminal, and
invalidate the temporary access permit at the end of communication
between the authorized communication terminal and the unauthorized
communication terminal.

3. The document browsing system as recited in claim 2, wherein the data
server transmits image data notifying non-grant of access to the
unauthorized communication terminal when the judgment received from the
authorized communication terminal refuses the access.

4. The document browsing system as recited in claim 2, wherein, the data
server transmits a session ID of the document data, to which the
unauthorized communication terminal is requesting the access, to the
unauthorized communication terminal; the unauthorized communication
terminal includes the session ID in the request for access permit when
transmitting the request for access permit to the authorized
communication terminal; the authorized communication terminal produces
the information for temporary access including the session ID that is
included in the request for access permit and ID data of the authorized
communication terminal, and transmits the information for temporary
access to the unauthorized communication terminal; the unauthorized
communication terminal produces the request for temporary access
including the session ID, the ID data of the authorized communication
terminal and ID data of the unauthorized communication terminal on the
basis of the information for temporary access, and transmits the request
for temporary access to the data server; the data server transmits the
information for judgment including the session ID included in the request
for temporary access the authorized communication terminal; and the
judging section permits the access if the session ID included in the
information for judgment is identical with a session ID of document data
which the authorized communication terminal is currently accessing, and
refuses the access if the session IDs are not identical.

5. The document browsing system as recited in claim 1, wherein, A1. the
authorized communication terminal comprises: a first data producer for
producing a request for producing information for temporary access, which
is requesting the data server to produce the information for temporary
access, upon receipt of the request for access permit from the
unauthorized communication terminal; and a first controller for
controlling the authorized communication terminal to transmit the request
for producing information for temporary access from the authorized
communication terminal to the data server and, upon receipt of the
information for temporary access from the data server, transmit the
information for temporary access from the authorized communication
terminal to the unauthorized communication terminal; A2. the unauthorized
communication terminal comprises: a second data producer for producing
the request for access permit and, upon receipt of the information for
temporary access from the authorized communication terminal, the request
for temporary access; and a second controller for controlling the
unauthorized communication terminal to transmit the request for access
permit to the authorized communication terminal and transmit the request
for temporary access to the data server; and B. the data server further
comprises: a third data producer for producing the information for
temporary access upon receipt of the request for producing information
for temporary access from the authorized communication terminal; and a
third controller for controlling the data server to transmit the
information for temporary access from the data server to the authorized
communication terminal, grant the unauthorized communication terminal a
temporary access permit upon receipt of the request for temporary access
from the unauthorized communication terminal, send the image data of the
document data to the unauthorized communication terminal only while the
authorized communication terminal is in communication with the
unauthorized communication terminal.

6. The document browsing system as recited in claim 1, wherein, A1. the
authorized communication terminal comprises: a first data producer for
producing the information for temporary access upon receipt of the
request for access permit from the unauthorized communication terminal;
and a first controller for controlling the authorized communication
terminal to transmit the information for temporary access from the
authorized communication terminal to the unauthorized communication
terminal and, upon receipt of authentication data from the data server
and a request for authentication from the unauthorized communication
terminal, transmit the authentication data to the unauthorized
communication terminal; A2. the unauthorized communication terminal
comprises: a second data producer for producing the request for access
permit and the request for authentication, and the request for temporary
access upon receipt of the information for temporary access from the
authorized communication terminal; and a second controller for
controlling the unauthorized communication terminal to transmit the
request for access permit and the request for authentication to the
authorized communication terminal, and the request for temporary access
and the authentication data as received from the authorized communication
terminal to the data server; and B. the data server further comprises: a
third data producer for producing the authentication data and a command
to request authentication, commanding the unauthorized communication
terminal to transmit the request for authentication to the authorized
communication terminal; and a third controller for controlling the data
server to transmit the command to request authentication to the
unauthorized communication terminal upon receipt of the request for
temporary access from the unauthorized communication terminal, transmit
the authentication data to the authorized communication terminal and, if
the authentication data from the unauthorized communication terminal is
identical with the authentication data as transmitted from the data
server to the authorized communication terminal, grant the unauthorized
communication terminal a temporary access permit and send the image data
of the document data to the unauthorized communication terminal only
while the authorized communication terminal is in communication with the
unauthorized communication terminal.

7. The document browsing system as recited in claim 1, wherein, the
request for access permit includes a session ID of the document data the
unauthorized communication terminal is requesting access, and ID data of
the unauthorized communication terminal; the information for temporary
access includes the session ID and ID data of the authorized
communication terminal; and the request for temporary access includes the
session ID, the ID data of authorized communication terminal, the ID data
of the unauthorized communication terminal, and set resolution data of
the unauthorized communication terminal, wherein, the data server
converts the document data to image data in accordance with the set
resolution data and sends the image data to the unauthorized
communication terminal when the access of the unauthorized communication
terminal to the document data is permitted.

8. A method of controlling a document browsing system that comprises a
data server and multiple communication terminals having image data
displaying function, the data server comprising a storage device storing
document data, a data converter for converting the document data to image
data, an authenticator for individual authentication and authorization of
the communication terminals, a communicator for communicating with the
multiple communication terminals and sending the document data as image
data to a communication terminal authorized by the authenticator, and a
communication detector for detecting the state of communication between
the communication terminals, the controlling method comprising: producing
a request for access permit, requesting an access to the document data,
at an unauthorized communication terminal that is not authorized by the
authenticator; transmitting the request for access permit to the
authorized communication terminal; producing information for temporary
access on the basis of the request for access permit from the
unauthorized communication terminal, in order to grant the unauthorized
communication terminal a temporary access permit; transmitting the
information for temporary access from the authorized communication
terminal to the unauthorized communication terminal; producing a request
for temporary access on the basis of the information for temporary access
at the unauthorized communication terminal; transmitting the request for
temporary access to the data server; judging whether to permit the
unauthorized communication terminal a temporary access to the document
data on the basis of information exchanged between the data server and
the authorized communication terminal; detecting the state of
communication of the authorized communication terminal at the data
server; sending image data of the same document data as sent to the
authorized communication terminal to the unauthorized communication
terminal if the temporary access of the unauthorized communication
terminal to the document data is permitted and the communication detector
detects that the authorized communication terminal is in communication
with the unauthorized communication terminal when the data server
receives the request for temporary access from the unauthorized
communication terminal; and invalidating the temporary access permit
given to the unauthorized communication terminal when the communication
detector detects the end of communication between the authorized
communication terminal and the unauthorized communication terminal.

9. The method of controlling the document browsing system as recited in
claim 8, further comprising: producing the information for temporary
access at the authorized communication terminal; producing information
for judgment on the basis of the request for temporary access at the data
server; transmitting the information for judgment from the data server to
the authorized communication terminal; making a judgment at the
authorized communication terminal, on the basis of the information for
judgment, as to whether the unauthorized communication terminal should be
permitted an access to the document data; transmitting the judgment from
the authorized communication terminal to the data server; and granting
the unauthorized communication terminal a temporary access permit if the
judgment permits the access.

10. The method of controlling the document browsing system as recited in
claim 8, further comprising: producing at the authorized communication
terminal a request for producing information for temporary access on the
basis of the request for access permit from the unauthorized
communication terminal; transmitting the request for producing
information for temporary access from the authorized communication
terminal to the data server; producing the information for temporary
access at the data server on the basis of the request for producing
information for temporary access; transmitting the information for
temporary access from the data server to the authorized communication
terminal; transmitting the information for temporary access from the
authorized communication terminal to the unauthorized communication
terminal; transmitting, on the basis of the information for temporary
access, the request for temporary access from the unauthorized
communication terminal to the data server; and granting the unauthorized
communication terminal a temporary access permit when the data server
receives the request for temporary access.

11. The method of controlling the document browsing system as recited in
claim 8, further comprising: producing the information for temporary
access at the authorized communication terminal on the basis of the
request for access permit from the unauthorized communication terminal;
transmitting the information for temporary access from the authorized
communication terminal to the unauthorized communication terminal;
producing at the dater server a command to request authentication,
commanding the unauthorized communication terminal to transmit a request
for authentication to the authorized communication terminal, on the basis
of the request for temporary access; transmitting the command to request
authentication from the data server to the unauthorized communication
terminal; producing the request for authentication at the unauthorized
communication terminal and transmitting the request for authentication to
the authorized communication terminal in response to the command to
request authentication; producing authentication data at the data server
on the basis of the request for temporary access; transmitting the
authentication data from the data server to the authorized communication
terminal; transmitting the authentication data from the authorized
communication terminal to the unauthorized communication terminal if a
session ID included in the request for authentication from the
unauthorized communication terminal is identical with a session ID of the
document data included in the authentication data and a session ID of
document data the authorized communication terminal is presently
accessing; transmitting the authentication data from the unauthorized
communication terminal to the data server; and granting the unauthorized
communication terminal a temporary access permit if the authentication
data received from the unauthorized communication terminal is identical
with the authentication data as transmitted from the data server to the
authorized communication terminal.

12. A data server communicable with multiple communication terminals
having data displaying function, the data server comprising: a storage
device storing document data; a data converter for converting the
document data to image data; an authenticator image data for individual
authentication and authorization of the multiple communication terminals;
a communicator for communicating with the multiple communication
terminals and transmitting the image data to a communication terminal
authorized by the authenticator; a temporary authorizer for authorizing,
upon receipt of a request for temporary access to the document data from
an unauthorized communication terminal that is not authorized by the
authenticator, as a temporarily-authorized communication terminal; a
communication detector for detecting the state of communication between
the communication terminals; and a controller for sending image data of
the same document data as sent to the authorized communication terminal
to the temporary unauthorized communication terminal when the
communication detector detects that the temporary authorized
communication terminal is in communication with the authorized
communication terminal, and invalidating the temporary authorization when
the communication detector detects that the temporarily-authorized
communication terminal does not communicate with the authorized
communication terminal.

13. The data server as recited in claim 12, wherein the temporary
authenticator authorizes the unauthorized communication terminal as a
temporarily-authorized communication terminal when the data server
receives ID data of the unauthorized communication terminal and the
request for temporary access from the unauthorized communication terminal
and also receives an access permit to the document data in association
with the ID data of the unauthorized communication terminal from the
authorized communication terminal.

14. The data server as recited in claim 12, comprising: a data producer
for producing information for temporary access in order to permit a
temporary access of the unauthorized communication terminal to the
document image data, the information for temporary access being
transmitted through the authorized communication terminal to the
unauthorized communication terminal, wherein, the temporary authenticator
authorizes the unauthorized communication terminal as a
temporarily-authorized communication terminal when the data server
receives the request for temporary access from the unauthorized
communication terminal, the request for temporary access being based on
the information for temporary access and including ID data of the
unauthorized communication terminal.

15. The data server as recited in claim 12, comprising: a data producer
for producing authentication data when the data server receives ID data
of the unauthorized communication terminal and the request for temporary
access from the unauthorized communication terminal, wherein, the
authentication data is transmitted to the authorized communication
terminal, transferred to the unauthorized communication terminal if the
authentication data is admitted to the authorized communication terminal,
and transmitted from the unauthorized communication terminal to the data
server; and the temporary authenticator authorizes the unauthorized
communication terminal as a temporarily-authorized communication terminal
when authentication data received from the unauthorized communication
terminal is identical with the authentication data as transmitted to the
authorized communication terminal.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a document browsing system, a
method of controlling the document browsing system and a data server for
the system.

[0003] 2. Description of the Related Art

[0004] As communication terminals that communicate with data servers
through the Internet to get access to document data stored in data
server, many kinds of mobile terminals such as mobile phones, smart
phones, and PDA (Personal Digital Assistant) terminals have recently been
widely spread. These communication terminals have a display device, such
as an LCD panel, for displaying data acquired from data servers. Document
data stored in data servers may include Word data created on Microsoft
Word, Excel data created on Microsoft Excel, CAD data created on Auto
CAD, graphic data, and any kinds of image data.

[0005] Concerning a data server for internal use only, stored document
data is converted to image data before sending the same to a
communication terminal in response to a request for access permit from
the communication terminal, in order to prevent the document data against
altering or tampering. Moreover, for security reason, the intra-company
data server is configured to give access permits to authorized
communication terminals only. However, it is sometimes necessary for
company employees to show their clients or visitors the same document as
the company employees are presently viewing on their authorized mobile
terminals at a meeting or conference. Not being authorized by the
intra-company data server, the mobile terminals of the customers cannot
receive image data of the same document data as the authorized mobile
terminals of the company employees can receive from the intra-company
data server. It may be possible for the visitors to view the image data
displayed on the authorized mobile terminals, or use a projector or a
large-screen monitor to display the image data received on an authorized
communication terminal on a large screen. However, the former solution is
inconvenient and inefficient, and the latter solution needs extra
equipment beside mobile terminals. Both solutions cannot work for remote
conference. JPA No. 2009-032212 discloses a browsing-approval file system
for confidential document, wherein a data server makes judgment as to
whether an application for browsing a confidential document should be
approved if the application is filed by an unauthorized terminal.

[0006] In the browsing-approval file system for confidential document of
the above patent document, only application-approved users are permitted
browsing the confidential documents. However, once the application for
approval of browsing from a user terminal has been approved by an
approver of the data server, the user terminal can thereafter access the
confidential document arbitrary without any approval in the prior system.
This may pose a threat to the security of the system.

[0007] The present invention is to solve the above problem and provide a
document browsing system and a controlling method for this system and a
data server of this system, whereby the same document data may be viewed
on multiple communication terminals without threatening the security of
confidential document data.

[0009] In view of the foregoing, an object of the present invention is to
provide a document browsing system, a method of controlling the document
browsing system and a data server for the system, wherein image data of
the same document data may be displayed simultaneously on multiple
communication terminals including those unauthorized by the data server
without weakening the security of the data browsing system.

[0012] an authorized communication terminal that is authorized by an
authenticator of the data server; and

[0013] an unauthorized communication terminal that is not authorized by
the authenticator; and

[0014] B. the data server comprises:

[0015] a storage device storing document data;

[0016] a data converter for converting the document data to image data;

[0017] the authenticator for authentication and authorization of the
communication terminals;

[0018] a communicator for communicating with the multiple communication
terminals and sending the image data to the authorized communication
terminal; and

[0019] a communication detector for detecting the state of communication
between the communication terminals, and wherein

[0020] C. the authorized communication terminal transmits information for
temporary access to the unauthorized communication terminal upon receipt
of a request for access permit from the unauthorized communication
terminal requesting an access to the document data, the information for
temporary access being used for granting the unauthorized communication
terminal a temporary access permit, and exchanges information with the
data server to decide whether the unauthorized communication terminal
should be allowed to access the document data;

[0021] the unauthorized communication terminal transmits the request for
access permit to the authorized communication terminal when requesting an
access to the document data, produces a request for temporary access on
the basis of the information for temporary access as received from the
authorized communication terminal, and transmits the request for
temporary access to the data server; and

[0022] the data server sends image data of the same document data as sent
to the authorized communication terminal to the unauthorized
communication terminal if the temporary access of the unauthorized
communication terminal to the document data is permitted on the basis of
the information exchanged between the data server and the authorized
communication terminal when the request for temporary access is received
from the unauthorized communication terminal and the communication
detector detects that the authorized communication terminal is in
communication with the unauthorized communication terminal, and the data
server invalidates the temporary access permit given to the unauthorized
communication terminal when the communication detector detects the end of
communication between the authorized communication terminal and the
unauthorized communication terminal.

[0023] In a preferred embodiment,

[0024] A1. the authorized communication terminal comprises:

[0025] a first data producer for producing the information for temporary
access upon receipt of the request for access permit from the
unauthorized communication terminal; and

[0026] a judging section for judging whether to grant the unauthorized
communication terminal the temporary access permit or not; and

[0027] a first controller for controlling the authorized communication
terminal to transmit the information for temporary access to the
unauthorized communication terminal and transmit the judgment by the
judging section to the data server;

[0028] A2. the unauthorized communication terminal comprises:

[0029] a second data producer for producing the request for access permit
and, upon receipt of the information for temporary access from the
authorized communication terminal, the request for temporary access; and

[0030] a second controller for controlling the unauthorized communication
terminal to transmit the request for access permit to the authorized
communication terminal and transmit the request for temporary access to
the data server; and

[0031] B. the data server further comprises:

[0032] a third data producer for producing information for judgment by the
judging section in the authorized communication terminal upon receipt of
the request for temporary access from the unauthorized communication
terminal; and

[0033] a third controller for controlling the data server to transmit the
information for judgment to the authorized communication terminal, send
the image data of the document data to the unauthorized communication
terminal when the judgment received from the authorized communication
terminal permits the access and the authorized communication terminal is
in communication with the unauthorized communication terminal, and
invalidate the temporary access permit at the end of communication
between the authorized communication terminal and the unauthorized
communication terminal.

[0034] The data server preferably transmits image data notifying non-grant
of access to the unauthorized communication terminal when the judgment
received from the authorized communication terminal refuses the access.

[0035] The data server preferably transmits a session ID of the document
data, to which the unauthorized communication terminal is requesting the
access, to the unauthorized communication terminal; the unauthorized
communication terminal preferably includes the session ID in the request
for access permit when transmitting the request for access permit to the
authorized communication terminal; and the authorized communication
terminal produces the information for temporary access including the
session ID that is included in the request for access permit and ID data
of the authorized communication terminal, and transmits the information
for temporary access to the unauthorized communication terminal.
According to this embodiment, the unauthorized communication terminal
produces the request for temporary access including the session ID, the
ID data of the authorized communication terminal and ID data of the
unauthorized communication terminal on the basis of the information for
temporary access, and transmits the request for temporary access to the
data server; the data server transmits the information for judgment
including the session ID included in the request for temporary access the
authorized communication terminal; and the judging section permits the
access if the session ID included in the information for judgment is
identical with a session ID of document data which the authorized
communication terminal is currently accessing, and refuses the access if
the session IDs are not identical.

[0036] In another preferred embodiment,

[0037] A1. the authorized communication terminal comprises:

[0038] a first data producer for producing a request for producing
information for temporary access, which is requesting the data server to
produce the information for temporary access, upon receipt of the request
for access permit from the unauthorized communication terminal; and

[0039] a first controller for controlling the authorized communication
terminal to transmit the request for producing information for temporary
access from the authorized communication terminal to the data server and,
upon receipt of the information for temporary access from the data
server, transmit the information for temporary access from the authorized
communication terminal to the unauthorized communication terminal;

[0040] A2. the unauthorized communication terminal comprises:

[0041] a second data producer for producing the request for access permit
and, upon receipt of the information for temporary access from the
authorized communication terminal, the request for temporary access; and

[0042] a second controller for controlling the unauthorized communication
terminal to transmit the request for access permit to the authorized
communication terminal and transmit the request for temporary access to
the data server; and

[0043] B. the data server further comprises:

[0044] a third data producer for producing the information for temporary
access upon receipt of the request for producing information for
temporary access from the authorized communication terminal; and

[0045] a third controller for controlling the data server to transmit the
information for temporary access from the data server to the authorized
communication terminal, grant the unauthorized communication terminal a
temporary access permit upon receipt of the request for temporary access
from the unauthorized communication terminal, send the image data of the
document data to the unauthorized communication terminal only while the
authorized communication terminal is in communication with the
unauthorized communication terminal.

[0046] In a further preferred embodiment,

[0047] A1. the authorized communication terminal comprises:

[0048] a first data producer for producing the information for temporary
access upon receipt of the request for access permit from the
unauthorized communication terminal; and

[0049] a first controller for controlling the authorized communication
terminal to transmit the information for temporary access from the
authorized communication terminal to the unauthorized communication
terminal and, upon receipt of authentication data from the data server
and a request for authentication from the unauthorized communication
terminal, transmit the authentication data to the unauthorized
communication terminal;

[0050] A2. the unauthorized communication terminal comprises:

[0051] a second data producer for producing the request for access permit
and the request for authentication, and the request for temporary access
upon receipt of the information for temporary access from the authorized
communication terminal; and

[0052] a second controller for controlling the unauthorized communication
terminal to transmit the request for access permit and the request for
authentication to the authorized communication terminal, and the request
for temporary access and the authentication data as received from the
authorized communication terminal to the data server; and

[0053] B. the data server further comprises:

[0054] a third data producer for producing the authentication data and a
command to request authentication, commanding the unauthorized
communication terminal to transmit the request for authentication to the
authorized communication terminal; and a third controller for controlling
the data server to transmit the command to request authentication to the
unauthorized communication terminal upon receipt of the request for
temporary access from the unauthorized communication terminal, transmit
the authentication data to the authorized communication terminal and, if
the authentication data from the unauthorized communication terminal is
identical with the authentication data as transmitted from the data
server to the authorized communication terminal, grant the unauthorized
communication terminal a temporary access permit and send the image data
of the document data to the unauthorized communication terminal only
while the authorized communication terminal is in communication with the
unauthorized communication terminal.

[0055] A method of controlling the document browsing system according to
the present invention comprises:

[0056] producing a request for access permit, requesting an access to the
document data, at an unauthorized communication terminal that is not
authorized by the authenticator;

[0057] transmitting the request for access permit to the authorized
communication terminal;

[0058] producing information for temporary access on the basis of the
request for access permit from the unauthorized communication terminal,
in order to grant the unauthorized communication terminal a temporary
access permit;

[0059] transmitting the information for temporary access from the
authorized communication terminal to the unauthorized communication
terminal;

[0060] producing a request for temporary access on the basis of the
information for temporary access at the unauthorized communication
terminal;

[0061] transmitting the request for temporary access to the data server;

[0062] judging whether to permit the unauthorized communication terminal a
temporary access to the document data on the basis of information
exchanged between the data server and the authorized communication
terminal;

[0063] detecting the state of communication of the authorized
communication terminal at the data server;

[0064] sending image data of the same document data as sent to the
authorized communication terminal to the unauthorized communication
terminal if the temporary access of the unauthorized communication
terminal to the document data is permitted and the communication detector
detects that the authorized communication terminal is in communication
with the unauthorized communication terminal when the data server
receives the request for temporary access from the unauthorized
communication terminal; and

[0065] invalidating the temporary access permit given to the unauthorized
communication terminal when the communication detector detects the end of
communication between the authorized communication terminal and the
unauthorized communication terminal.

[0066] A data server of the present invention comprises:

[0067] a storage device storing document data;

[0068] a data converter for converting the document data to image data;

[0069] an authenticator image data for individual authentication and
authorization of the multiple communication terminals;

[0070] a communicator for communicating with the multiple communication
terminals and transmitting the image data to a communication terminal
authorized by the authenticator;

[0071] a temporary authorizer for authorizing, upon receipt of a request
for temporary access to the document data from an unauthorized
communication terminal that is not authorized by the authenticator, as a
temporarily-authorized communication terminal;

[0072] a communication detector for detecting the state of communication
between the communication terminals; and

[0073] a controller for sending image data of the same document data as
sent to the authorized communication terminal to the temporary
unauthorized communication terminal when the communication detector
detects that the temporary authorized communication terminal is in
communication with the authorized communication terminal, and
invalidating the temporary authorization when the communication detector
detects that the temporarily-authorized communication terminal does not
communicate with the authorized communication terminal.

[0074] According to the present invention, an unauthorized communication
terminal can get access to the document data stored in the data server
only when the authorized communication terminal and the data server
authenticate the unauthorized communication terminal and grant the
unauthorized communication terminal a temporary access permit. Moreover,
the data server invalidates the temporary access permit when the
unauthorized communication terminal is disconnected from the authorized
communication terminal. Therefore, image data of the same document data
may be displayed simultaneously on multiple communication terminals
including those unauthorized by the data server, while assuring the
security of the data browsing system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0075] The above and other objects and advantages of the present invention
will be more apparent from the following detailed description of the
preferred embodiments when read in connection with the accompanied
drawings, wherein like reference numerals designate like or corresponding
parts throughout the several views, and wherein:

[0077] FIG. 2 is a block diagram illustrating electric structures of first
and second mobile phones;

[0078] FIG. 3 is a plan view illustrating an LCD screen displaying first
image data on a first mobile phone;

[0079]FIG. 4 is a plan view illustrating an LCD screen of a second mobile
phone, displaying image data notifying non-grant of access;

[0080] FIG. 5 is a flowchart illustrating a processing sequence for the
document data browsing system in accordance with a first embodiment;

[0081] FIG. 6 is a flowchart illustrating a processing sequence for the
document data browsing system in accordance with a second embodiment; and

[0082] FIG. 7 is a flowchart illustrating a processing sequence for the
document data browsing system in accordance with a third embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

[0083] Referring to FIGS. 1 and 2, a document browsing system 2 includes a
data server 10 and multiple communication terminals including a first
mobile phone 11 and a second mobile phone 12. Respective mobile phones 11
and 12 are communicable with the data server 10 through the Internet 15.

[0084] The data server 10 includes a communicator 21 for establishing
communication with the mobile phones 11 and 12 through the Internet 15, a
database (DB) 22 storing numbers of sets of document data, including Word
data, Excel data, CAD data, graphic data, PDF data etc., a database (DB)
controller 23, a CPU 24, an authenticator 25 for authenticating
individual communication terminals and approving an access to the
document data. The data server 10 also includes a data converter 26 for
converting the format of document data or the resolution of image data, a
data producer 27 for producing information for use in permitting a
temporary access to the document data, a communication detector 28 for
detecting the state of communication between the mobile phones 11 and 12,
and a memory 29. These components are connected through a data bus 20 to
the CPU 2 so that the CPU 24 totally controls these components. An
individual session ID is assigned to each set of document data.

[0085] The memory 29 memorizes ID data of those communication terminals
which have been authorized to access the document data. The authenticator
25 judges whether ID data of a communication terminal that requests an
access to the document data is included in the ID data of authorized
communication terminals memorized in the memory 29. According the present
embodiment, the first mobile phone 11 is of an employee of a particular
company that owns the data server 10 and hence the first mobile phone 11
is authorized by the authenticator 25, whereas the second mobile phone 12
is of a client who visits the particular company and is not authorized by
the authenticator 25.

[0086] The first mobile phone 11 is provided with a power button 31,
multiple input buttons 32, a menu key 33 for the user to set up and
select various modes and operations, and make decisions, and an LCD 34.
The first mobile phone 11 is provided with a communicator 35 for wireless
communication with base stations and communication with the data server
10 through the Internet 15, a CPU 36 for controlling the first mobile
phone 11, a memory 37, a short-distance communicator 38 for establishing
communication with another communication terminal, like the second mobile
phone 12, according to the well-known Bluetooth (trade name) protocol,
and a data producer 39 for producing information for use in permitting a
temporary access to the document data. The LCD 34 may for example display
an image in 480×854-dot pixel size, and data of the set resolution
of the LCD 34 is memorized in the memory 37.

[0087] Like the first mobile phone 11, the second mobile phone 12 is
provided with a power button 41, input buttons 42, a menu key 43, an LCD
44, a communicator 45 for wireless-communication and communication over
the Internet, a CPU 46, a memory 47, a short-distance communicator 48,
and a data producer 49. The LCD 44 may for example display an image in
240×400-dot pixel size, and data of the set resolution of the LCD
44 is memorized in the memory 47.

[0088] The mobile phones 11 and 12 are provided with a telephone mode for
making a call to a fixed-line phone or another mobile phone, and a
communication mode for establishing communication with the data server 10
and other mobile phones.

[0089] Telephone numbers may be registered in the memory 37. When a
telephone number is read out from the memory 37 through the menu key 33,
or a telephone number is input through the input buttons 32, the
communicator 35 establishes a wireless communication with a base station
of the mobile phone company, enabling making a call to a fixed-line phone
or another mobile phone through not-shown microphone and speaker built in
the first mobile phone 11.

[0090] When the communication mode is selected through the menu key 33 and
an URL address of the data server 10 is entered or read out from the
memory 37, the first mobile phone 11 is connected to the data server 10
through the Internet 15. In communication mode, the first mobile phone 11
transmits ID data thereof and the set resolution data of the LCD 34 to
the data server 10. Since the ID data of the first mobile phone 11 is
registered as authenticated ID in the memory 29 of the data server 10,
the authenticator 25 permits an access of the first mobile phone 11 to
any document data stored in the database 22.

[0091] By operating the menu key 33, a set of document data (e.g., a set
of Word data containing ten pages of a document) may be selected from
among many sets of document data stored in the database 22. Then the
database controller 23 transmits the selected document data to the data
converter 26. The data converter 26 converts the selected document data
to first image data of a pixel in accordance with the set resolution of
the LCD 34, so that the first image data may be suitably displayed on the
LCD 34 (480×854 in pixel size). In the present example wherein the
document data is assumed to be Word data consisting of ten pages, the
first image data also consists of ten pages. Note that the same control
as for Word data is executed with respect to Excel data, graphic data
etc.

[0092] The first image data is transmitted through the communicator 21 and
the Internet 15 to the first mobile phone 11. The first image data is
received on the communicator 35, and the first page thereof is displayed
on the LCD 34, as shown in FIG. 3.

[0093] The second mobile phone 12 is controlled in the same way as the
first mobile phone 11 in the telephone mode. In the communication mode,
however, the second mobile phone 12 is not authorized by the
authenticator 25 and is not usually allowed to access and download the
document data stored in the data server 10. In order to view the document
data in the data server 10, the user of the second mobile phone 12 has to
operate the menu key 33 to select one document from among many documents
stored in the database 22. Then, the database controller 23 reads out a
session ID of the selected document and transmits the read session ID
from the communicator 21 to the second mobile phone 12. Upon receipt of
the session ID from the data server 10, the second mobile phone 12
produces a request for access permit in the data producer 49 and
transmits the same to the first mobile phone 11. This request for access
permit includes the URL address of the database 22, the session ID of the
requested document and ID data of the second mobile phone 12.

[0094] Upon receipt of the request for access permit from the second
mobile phone 12, the first mobile phone 11 produces information for
temporary access in the data producer 39 and transmits the information to
the second mobile phone 12. The information for temporary access includes
the URL address, the session ID of the requested document data and ID
data of the first mobile phone 11, and is used for permitting a temporary
access to the document data of which the session ID is included in the
request for access permit.

[0095] Upon receipt of the information for temporary access, the second
mobile phone 12 is connected to the data server 10 of the URL address as
included in the information for temporary access over the Internet 15. At
the same time, the second mobile phone 12 produces a request for
temporary access, which includes the session ID of the document data, the
ID of the first mobile phone 11, ID data of the second mobile phone 12
and data of set resolution of the LCD 44, in the data producer 49 and
transmits the request for temporary access to the data server 10.

[0096] Upon receipt of the request for temporary access, the data producer
27 of the data server 10 produces information for judgment as to whether
the request for temporary access is approved or not, and the data server
10 transmits the information for judgment to the first mobile phone 11
with reference to the ID of the first mobile phone 11 included in the
request for temporary access. The information for judgment includes the
session ID and the ID of the second mobile phone 12, which are included
in the request for temporary access from the second mobile phone 12.

[0097] the CPU 36 of the first mobile phone 11 makes a judgment based on
the information for judgment as to whether the request for temporary
access is approved or not. The first mobile phone 11 produces a notice of
grant of access in the data producer 39 if the session ID included in the
information for judgment is identical to a session ID of a document of
which image data is presently displayed on the first mobile phone 11,
permitting a temporary access of the second mobile phone 12 to the
requested document and instructing the data server 10 to send image data
of the requested document to the second mobile phone 12. The notice of
grant of access includes the session ID as included in the information
for judgment from the data server 10 and the ID of the second mobile
phone 12.

[0098] When the data server 10 receives the notice of grant of access, the
CPU 24 of the data server 10 temporarily authorizes the second mobile
phone 12 on the basis of the ID of the second mobile phone 12. The
database controller 23 retrieves the document data as an origin of the
first image data with reference to the session ID included in the notice
of grant of access. Then the data converter 26 converts the retrieved
document data to second image data representing ten pages of the
retrieved document in accordance with the set resolution data of the LCD
44, the second image data being in compliance with the display format of
the LCD 44 of the second mobile phone 12. Thus, the second image data
represents the same document as the first image data sent to the first
mobile phone 11, though the pixel number of the second image data is
different from that of the first image data.

[0099] The communication detector 28 of the data server 10 detects the
state of communication of the first mobile phone 11, to send the second
image data to the second mobile phone 12 while the first mobile phone 11
is in communication with the second mobile phone 12. The CPU 46 of the
second mobile phone 12 controls displaying the received second image data
on the LCD 44.

[0100] On the other hand, if the session ID included in the information
for judgment is not identical with the session ID of the document
currently displayed on the first mobile phone 11, the first mobile phone
11 produces a notice of non-grant of access in the data producer 39 and
transmits the same to the data server 10. Note that, even once the first
mobile phone 11 has transmitted a notice of grant of access to the data
server 10, when the user of the first mobile phone 11 terminates viewing
the first image data or begins to browse other documents, the first
mobile phone 11 will issue a notice of non-grant of access and transmit
the same to the data server 10 because the session ID included in the
information for judgment is not anymore identical with a session ID of
the currently browsed document. When the notice of non-grant of access is
received after once the notice of grant of access has been received with
respect to the same case, the data server 10 invalidates the temporary
access permit given to the second mobile phone 12, and forcibly quits the
communication with the second mobile phone 12.

[0101] When the data server 10 receives the notice of non-grant of access,
the data converter 26 reads out document data notifying non-grant of
access from the database 22 and converts the same to image data of the
format compatible with the LCD 44. The image data notifying non-grant of
access is sent to the second mobile phone 12, and the CPU 46 of the
second mobile phone 12 controls displaying the received image data on the
LCD 44, as shown for example in FIG. 4.

[0102] When the communication detector 28 detects that the first mobile
phone 11 gets out of communication with the second mobile phone 12, the
data server 10 invalidates the temporary access permit of the second
mobile phone 12 to the requested document, and forcibly quits
communication with the second mobile phone 12.

[0103] The operation of the first embodiment will be described below with
reference to the flowchart of FIG. 5. First, the first mobile phone 11,
which is authorized to access any document data in the database 22 of the
data server 10, is switched to the communication mode, to connect with
the data server 10 through the Internet 15 (step S1). Thereafter, the
first mobile phone 11 is assumed to keep connection with the data server
10 in the following explanation.

[0104] In the communication mode, the first mobile phone 11 transmits the
ID data thereof and the set resolution data of the LCD 34 to the data
server 10 (S2). The ID data of the first mobile phone 11 is included in
the authenticated ID data stored in the memory 29 of the data server 10,
the authenticator 25 authenticates the first mobile phone 11 and permits
the first mobile phone to access any documents in the database 22. The
user of the first mobile phone 11 may select one document from among many
documents in the database 22 by operating the menu key 33. On the basis
of the set resolution data of the LCD 34, the data converter 26 of the
data server 10 converts data of the selected document to first image data
that is suitable for displaying on the LCD 34, i.e., 480×854-dot
image data in the present embodiment (S3).

[0105] The first image data is sent from the data server 10 through the
communicator 21 and the Internet 15 (S4) and is received on the
communicator 35 of the first mobile phone 11 (S5). The CPU 36 of the
first mobile phone 11 controls displaying the received first image data
on the LCD 34, as shown for example in FIG. 3 (S6).

[0106] The second mobile phone 12, unauthorized to access the document
data of the database 22 of the data server 10, is switched to the
communication mode, to connect with the data server 10 through the
Internet 15. Thereafter when the user operates the menu key 33 to select
one document from among many documents in the database 22, the database
controller 23 of the data server 10 reads the session ID of the selected
document and transmits the read session ID from the communicator 21 to
the second mobile phone 12. Then the second mobile phone 12 produces a
request for access permit that includes the received session ID, an URL
address of the selected document and the ID data of the second mobile
phone 12, and transmits the request for access permit from the
short-distance communicator 48 to the first mobile phone 11 (S7).

[0107] When the request for access permit from the second mobile phone 12
is received on the short-distance communicator 38 (S8), the first mobile
phone 11 sends back information for temporary access to the second mobile
phone 12. The information for temporary access includes the ID of the
first mobile phone 11, the URL address and the session ID included in the
request for access permit, and is used for temporarily permitting the
second mobile phone 12 to access the document data identified by the
session ID (S9).

[0108] Upon receipt of the information for temporary access (S10), the
second mobile phone 12 makes a connection through the Internet 15 to the
data server 10 on the basis of the URL address included in the
information for temporary access. The second mobile phone 12 also
produces a request for temporary access, which includes the session ID,
the ID of the first mobile phone 11, the ID of the second mobile phone 12
and the set resolution data of the LCD 44, in a data producer 49, and
transmits the request for temporary access to the data server 10 (S11).

[0109] Upon receipt of the request for temporary access, the data server
10 produces information for judgment executed in the first mobile phone
as to whether this request should be approved or not; the information for
judgment includes the session ID and the ID of the second mobile phone 12
and is transmitted to the first mobile phone 11 (S12).

[0110] Upon receipt of the information for judgment (S13), the first
mobile phone 11 judges whether the second mobile phone should be
permitted a temporary access to the requested document (S14). If the
session ID included in the information for judgment is identical to the
session ID of the document currently viewed on the first mobile phone 11
("YES" in S14), the first mobile phone 11 permits the temporary access of
the second mobile phone 12. If the session ID included in the information
for judgment is not identical to the session ID of the document currently
viewed on the first mobile phone 11 ("NO" in S14), the first mobile phone
11 does not permit the temporary access. Note that the same session ID is
assigned to one document even while the document contains more than one
page. Therefore, the temporary access of the second mobile phone is to be
permitted if the user is viewing any page of the document identified by
the same session ID as included in the information for judgment.

[0111] When the access is permitted ("YES" in S14), the first mobile phone
11 transmits a notice of a grant of access to the data server 10,
granting the second mobile phone 12 a temporary access to the document
data and instructing the data server 10 to send image data of the
requested document data to the second mobile phone 12 (S15). The notice
of grant of access includes the session ID and the ID of the second
mobile phone 12.

[0112] When the data server 10 receives the notice of grant of access (S16
and "YES" in S17), the CPU 24 temporarily authorizes the second mobile
phone 12 to access the document data on the basis of the ID of the second
mobile phone 12. The database controller 23 retrieves the document data
as the origin of the first image data on the basis of the session ID
included in the notice of grant of access. Then the data converter 26
converts the retrieved document data to second image data suitable for
the LCD 44 of the second mobile phone 12, i.e. 240×400-dot image
data in the present embodiment, on the basis of the set resolution data
of the LCD 44 included in the request for temporary access from the
second mobile phone 12 (S18).

[0113] The communication detector 28 of the data server 10 detects the
state of communication of the first mobile phone 11. When the
communication detector 28 detects that the first mobile phone 11 is in
communication with the second mobile phone 12 ("YES" in S19), the CPU 24
sends the second image data to the second mobile phone 12 (S20). The
second image data is received on the communicator 45 of the second mobile
phone 12 (S21).

[0114] When the second image data is received on the communicator 45 the
CPU 46 of the second mobile phone 12 controls displaying the second image
data on the LCD 44 (S24). Thus, the user of the second mobile phone 12
can view the same document data as the user of the first mobile phone 11
only when the first mobile phone 11 permits the second mobile phone 12 to
access the document data, which assures the security of the document
browsing system 2.

[0115] If, on the other hand, the first mobile phone 11 makes a judgment
against the access of the second mobile phone 12 to the database 22 ("NO"
in S14), the first mobile phone 11 notices the data server 10 of
non-grant of access (S22). Even once the first mobile phone 11 has
transmitted a notice of grant of access to the data server 10, when the
user of the first mobile phone 11 terminates viewing the first image data
or begins to browse other documents, the first mobile phone 11 will issue
a notice of non-grant of access and transmit the same to the data server
10 because the session ID included in the information for judgment is not
anymore identical with a session ID of the currently browsed document.
When the notice of non-grant of access is received after once the notice
of grant of access has been received with respect to the same case, the
data server 10 invalidates the temporary access permit given to the
second mobile phone 12, and forcibly quits the communication with the
second mobile phone 12 (S25). When the data server 10 receives the notice
of non-grant of access (S16 and "NO" in S17), the document data notifying
non-grant of access is converted to image data suitable for the LCD 44,
and the image data notifying non-grant of access is sent to the second
mobile phone 12 (S23). As a result, the image data notifying the
non-grant of access, as shown for example in FIG. 4, is displayed on the
LCD 44 (S24).

[0116] When the communication detector 28 detects that the first mobile
phone 11 gets out of communication with the second mobile phone 12 ("NO"
in S19), the data server 10 invalidates the temporary access permit of
the second mobile phone 12 to the document data, and forcibly quits
communication with the second mobile phone 12 (S25). Thus, even after
being permitted access to the same document data as the user of the first
mobile phone 11 is currently viewing, the user of the second mobile phone
12 can view the document data only while the second mobile phone 12 is in
communication with the first mobile phone 11 and the same document is
being displayed on both the first and second mobile phones 11 and 12.
Therefore, the security of the document browsing system is still more
tightened.

Second Embodiment

[0117] The second embodiment shown in FIG. 6 is configured to produce
information for temporary access in the data server 10, wherein the same
or equivalent components are designated by the same reference numbers as
in the first embodiment and the detailed description of these components
will be omitted to avoid redundancy.

[0118] The first mobile phone 11 is connected to the data server 10
through the Internet 15 when switched to the communication mode (S101).
Following steps S102 to S107 are equivalent to the steps S2 to S7 of
first embodiment; the description of these steps will be skipped.

[0119] When the first mobile phone 11 receives a request for access permit
from the second mobile phone 12 (S108), the data producer 39 of the first
mobile phone 11 produces a request for producing information for
temporary access, requesting the data server 10 to produce information
for temporary access, and the request for producing information for
temporary access is transmitted to the data server 10 (S109). When the
request for producing information for temporary access is received on the
communicator 21 of the data server 10, the data producer 27 of the data
server 10 produces information for temporary access (S110). The
information for temporary access includes the URL address and the session
ID of the requested document data and is transmitted to the first mobile
phone 11 (S111). Note that the session ID included in the information for
temporary access is effective only for an access from the second mobile
phone 12.

[0120] When the first mobile phone 11 receives the information for
temporary access (S112), the first mobile phone 11 transmits the received
information for temporary access to the second mobile phone 12 (S113).

[0121] Upon receipt of the information for temporary access (S114), the
second mobile phone 12 makes a connection to the data server 10 through
the Internet 15 with reference to the URL address included in the
information for temporary access, and produces a request for temporary
access by including ID data of the second mobile phone 12 and the set
resolution data of the LCD 44 of the second mobile phone 12. The
information for temporary access is transmitted from the second mobile
phone 12 to the data server 10 (S115).

[0122] When the data server 10 receives the request for temporary access,
the CPU 24 temporarily authorizes the second mobile phone 12 on the basis
of the ID of the second mobile phone 12 included in the request for
temporary access. On the basis of the session ID included in the request
for temporary access from the second mobile phone 12, the database
controller 23 retrieves document data as the origin of the first image
data that has been sent to the first mobile phone 11. The data converter
26 converts the retrieved document data to second image data in
accordance with the set resolution data of the LCD 44 (S116). When the
communication detector 28 detects that the first mobile phone 11 is in
communication with the second mobile phone 12 ("YES" in S117), the second
image data is sent to the second mobile phone 12 (S118), received on the
communicator 45 (S119) and displayed on the LCD 44 of the second mobile
phone 12 (S120).

[0123] When the first mobile phone 11 gets out of communication with the
second mobile phone 12 ("NO" in S117), the CPU 24 of the data server 10
invalidates the temporary access permit of the second mobile phone 12 and
forcibly quits communication with the second mobile phone 12 (S121).

Third Embodiment

[0124] According to the third embodiment shown in FIG. 7, authentication
data produced in the data server 10 is transmitted to the second mobile
phone 12 by way of the first mobile phone 11, wherein the same or
equivalent components are designated by the same reference numbers as in
first embodiment, so that the detailed description of these components
will be omitted.

[0125] In the communication mode, the first mobile phone 11 is connected
to the data server 10 through the Internet 15 (S201). Following steps
S202 to S211 are equivalent to the steps S2 to S11 of the first
embodiment; the description of these steps will be skipped.

[0126] When the data server 10 receives a request for temporary access
from the second mobile phone 12, a command to request authentication is
produced in the data producer 27 of the data server 10. The command to
request authentication is transmitted to the second mobile phone 12,
instructing the second mobile phone 12 to transmit a request for
authentication to the first mobile phone (S212).

[0127] In response to the command to request authentication (S213), the
second mobile phone 12 produces a request for authentication in the data
producer 49 and transmits the same to the first mobile phone 11 (S214).
The request for authentication includes the URL address and the session
ID of the document data to which the second mobile phone 12 has applied
for an access.

[0128] After transmitting the command to request authentication to the
second mobile phone 12, the data server 10 transmits authentication data
to the first mobile phone 11 in order to give a temporary access permit
to the second mobile phone 12 (S215). The authentication data includes
the session ID and the ID of the second mobile phone 12 included in the
request for temporary access. Thus, the first mobile phone 11 receives
the authentication data from the data server 10 (S216) and, at the same
time, the request for authentication from the second mobile phone 12. If
the session ID included in the request for authentication is identical
with the session ID included in the authentication data, and is also
identical with a session ID of a document currently viewed on the first
mobile phone 11 ("YES" in S217), the first mobile phone 11 transmits the
authentication data to the second mobile phone 12 (S218).

[0129] Upon receipt of the authentication data (S219), the second mobile
phone 12 transmits the authentication data to the data server 10 (S220).

[0130] When the data server 10 receives the authentication data from the
second mobile phone 12 (S221), the CPU 24 makes a judgment as to whether
the second mobile phone 12 is permitted a temporary access (S222). If the
authentication data from the second mobile phone 12 is identical with the
authentication data that the data server 10 has transmitted to the first
mobile phone 11 ("YES" in S222), the second mobile phone 12 is
authenticated and temporarily authorized to access the document data. If
not ("NO" in S222), the second mobile phone 12 is not authenticated.

[0131] If the temporary access is permitted ("YES" in S222), the database
controller 23 retrieves document data as the origin of the first image
data on the basis of the session ID included in the request for temporary
access from the second mobile phone 12. Then the data converter 26
converts the retrieved document data to the second image data in
accordance with the set resolution data of the LCD 44 (S223). If the data
communicator 28 detects that the first mobile phone 11 is in
communication with the second mobile phone 12 ("YES" in S224), the second
image data is sent to the second mobile phone 12 (S225) and received on
the communicator 45 of the second mobile phone 12 (S226). The received
second image data is displayed on the LCD 44 (S228).

[0132] If, on the other hand, the temporary access is not permitted ("NO"
in S222), the data converter 26 converts the document data notifying
non-grant of access to image data suitable for the LCD 44, and the image
data notifying non-grant of access is sent to the second mobile phone 12
(S227), and is displayed on the LCD 44 (S228).

[0133] When the communication detector 28 of the data server 10 detects
that the first mobile phone 11 gets out of communication with the second
mobile phone 12 ("NO" in S224), the CPU 24 invalidates the temporary
authorization of the second mobile phone 12, and forcibly quits
communication with the second mobile phone 12 (S229).

[0134] In the above embodiments, the access to the document is permitted
in the unit of one set of document data representative of the whole
document, i.e. all pages of the document data. However, it may be
possible to make the judgment on each individual page of the document
data and send image data of each page to the temporarily-authorized
mobile phone. In that case, a session ID should be given to each page of
the document data, and image data of one page is sent to the
temporarily-authorized mobile phone only while the one page is displayed
on the authorized mobile phone.

[0135] In the above embodiments, data of set resolution of each LCD of the
individual communication terminal is transmitted to the data server so
that the data converter may convert document data to image data in
accordance with the set resolution data. Alternatively, attribute data
specific to each communication terminal may be transmitted to the data
server so that the data converter may convert document data to image data
on the basis of the attribute data. Such attribute data may include the
name of manufacturer and the model number of the communication terminal.
In this embodiment, the data server should register data of respective
set resolutions of various communication terminals in the memory, so that
the data converter may read out the data of set resolutions in
association with the attribute data received from the requesting
communication terminal, to convert document data to image in accordance
with the read data.

[0136] Although the present invention have been described with reference
to the illustrated embodiments wherein two mobile phones are involved in
the document browsing system, the number of communication terminals may
change as appropriate. For example, first to fifth mobile phones may be
involved in the system of the present invention, among which the first
mobile phone is authorized and the second to fifth mobile phones are not
authorized. In that case, the first mobile phone and the data server may
apply the same processes to each of the second to fifth mobile phones as
applied to the second mobile phone in the above embodiments. It should be
understood that the embodiments of the present invention have been
described for illustrative purposes only. Those skilled in the art will
appreciate that various modifications, additions and substitutions are
possible without departing from the scope and spirit of the invention as
disclosed in the accompanying claims.